Method and apparatus for photon-assisted evaluation of a plasma

Abstract

Described are a method and apparatus for evaluating a least one characteristic of a plasma. The described method uses photons to raise the excitation state to or past the point of ionization of atoms which will traverse the plasma to be evaluated. The ionization of the atoms, followed by the measurement of the energy of any resulting secondary ions, facilitates the determining of one or more characteristics of the plasma. In one example, the photons are provided by a laser which directs a beam to intersect, and in some examples to be collinear with, a beam of atoms directed through the plasma.

Description

BACKGROUND OF THE INVENTION[0001]The present invention relates generally to methods and apparatus that may be used for evaluating a plasma, and more specifically relates to such methods and apparatus providing improved evaluating of plasmas, particularly those for which previous measurement techniques have offered less than optimal results.[0002]A number of systems have been used or considered for evaluating of plasmas formed in chambers or similar devices. In many circumstances the systems have been configured to measure relatively high temperature and / or high density plasmas. For example, systems such as Heavy Ion Beam Probes have been used for such purposes. While different configurations of Heavy Ion Beam Probe systems are known for evaluating different types of plasma devices, in general, such systems operate by directing an ionized beam through the plasma, where the ions will become “heavy ions” through electron impact within the plasma, thereby becoming “doubly ionized.” The ...

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Benefits of technology

[0007]The present invention utilizes a photon source to assist ionization of atoms used for evaluating at least one characteristic of a plasma. In the described examples of the invention, a beam of neutral atoms (“neutrals”) will be directed toward the plasma, and some portion of those neutrals will be excited, and in some preferred examples ionized, through interaction with photons from a photon source such as, in some examples, a laser. Through th

Problems solved by technology

One limitation of such Heavy Ion Beam Probe systems is that the incident electron impact energy must be equal to or greater than the second stage ionization potential of the ions in the beam.

Thus, a significant limitation on such Heavy Ion Beam Probe systems is that they are not suitable for use with relatively low temperature plasmas, for example, plasmas operating at approximately 1-2 eV.

Such plasmas typically do not have enough sufficiently hot electrons to achieve significant second stage ionization in the ion beam, and thus signal levels are generally very low.

This limitation on such probe systems is significant particularly to industries such as the semiconductor manufacturing industry, which typically uses “cold plasmas,” that is plasmas with electron temperatures of approximately 2 electron volts or less.

With such probes, however, the measurements are less than optimal because the mere presence of the Langmuir probe disrupts the plasma to at least some degree.

Additionally, the measurement may only be made at a single point in the plasma, and is often believed to be inaccurate.

Additionally, a varying plasma gradient across the wafer may create localized plasma charging resulting in damage to the structures formed, such as the gate oxide layer.

Accordingly, for that industry, the currently-available techniques do not provide either a system capable of measuring the relatively cold plasmas that are typically of interest, or a mechanism for identifying any irregularities or discontinuities in plasma characteristics across the wafer dimension.

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